1. Field of the Invention
This invention relates to a method of electrolytically graining an aluminum plate, and more particularly to an electrolytic graining method which comprises passing an alternating current through an aluminum plate in an acidic electrolyte.
2. Description of the Prior Art
Aluminum plates have hitherto been used as supports for lithographic printing plates, and the surface thereof is usually grained for the purpose of increasing the adhesion force between the surface and a light-sensitive layer provided thereon, and improving the property of retaining a fountain solution which is applied at the time of printing.
With respect to such graining methods, mechanical graining methods, e.g., a ball graining method and a brush graining method, have long been known. Recently, however, attention has increasingly been paid to an electrolytic graining method, which is a method comprising electrolytically etching a surface of an aluminum plate by passing an alternating current through the aluminum plate in an acidic electrolyte, such as hydrochloric acid, nitric acid or the like.
This electrolytic graining method enables attainment of an aluminum plate having a uniformly grained surface which has a greater graininess than those obtained by conventional mechanical graining methods. Such a grained surface, however, can be obtained only under particular conditions: that is, although grained products having uniform performance can be obtained by controlling various conditions, including the composition of an electrolyte, the temperature, the electrolytic conditions, etc., it is required to control the electrolytic conditions precisely within a narrow range. It is, therefore, very difficult to effect an electrolytic graining method while controlling the electrolytic conditions within such a narrow range.
Furthermore, the graining of aluminum plates by the electrolytic graining method consumes a large quantity of electricity. Recently, therefore, the ratio of electricity costs to the overall production costs of printing plates has been increasing, which is undesirable from an economic viewpoint.